1. Field of the Invention
The present invention relates to a laminated glazing panel, comprising at least two sheets of glass, and to its manufacturing process.
2. Discussion of the Background
The invention will be more particularly described in the case of use as a window for a vessel for cooking under pressure, such as a pressure cooker, but it is not limited to such an application; a glazing panel according to the invention may also be used as a window pane or window for vessels where one or more of the following properties may be required: withstanding pressure and, temperature and moisture resistance. The glazing panel according to the invention may also be used under conditions requiring none of these properties.
The glazing panel according to the invention may especially be used as a window pane or window for an integrated or external steam generator which can be used for a multitude of appliances, especially domestic appliances such as irons, steam cleaners, steam ovens, etc.
Although it is not usual to find windows on pressure cookers, it turns out that consumer demand has led manufacturers of these devices to devise such an improvement. This improvement, or more precisely this change, allows the consumer to monitor the food during cooking and also enables him to satisfy his curiosity since he can see the rapid change in the cooking of the food, this change normally being invisible since this type of device is impervious to light.
Such a change in these devices has already been proposed, especially in European Patent Application 298,405. This document describes a lid for a vessel for cooking under pressure suitable for closing or sealing off a cooking appliance of the pressure-cooker type. According to this document, the lid includes an opening closed off by a glazing panel composed of two sheets of glass bonded to each other by a bonding product based on a transparent polybutadiene synthetic rubber. The lid presented in this document enables the inside of the appliance to be seen, but the extent of this remains very limited; this is because it appears that, in use, the device proposed only enables the production of windows having a limited diameter, allowing only very limited viewing. The approach of one's face limits the passage of light. These restricted dimensions are especially due to limited mechanical properties of the glazing panel. This document provides solutions, especially described in FIGS. 19 and 20, which get round the problem of a lack of light either by creating a second window, through which light penetrates, or by installing an electrical device which illuminates the inside of the vessel. Either of these solutions is highly advantageous, but enormously complicates the production of the appliance and considerably increases the manufacturing costs.
Moreover, it appears that at high temperatures the glazing panel forming the window deteriorates. The term "high temperatures" is understood to mean temperatures which are greater than the normal use temperatures but which may in particular be reached during misuse, for example when there is no water present. Deterioration of the glazing panel is in fact a problem more directly associated with the bonding layer based on polybutadiene synthetic rubber since, when such temperatures are reached in the cooking appliance, the bonding layer becomes brownish in color and crazes. Its function, which is to allow one to look into the appliance, is therefore no longer fulfilled. Replacement of the window is then necessary and therefore leads to an additional cost. Moreover, this replacement is obviously not a simple operation and requires the article to be returned to the factory, an operation costly in terms of time and money; it is clear that such a window requires special and rigorous mounting in order to be able to withstand the pressures which may prevail in the cooking appliance.